Validity2 - 1 Evaluation of Experiments Reliability of...

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Evaluation of Experiments
Reliability of Measures
Consistency, repeatability
The major forms of reliability estimate:
1. Test - retest. Give the same test to the same people at some later time, and compute the
correlation. Time lag varies.
2. Alternate forms. Two forms of the test (form A, form B) are developed and given at the
same time to a group of people.
3. Internal consistency. One test is given once. The individual items themselves or else
groups of items serve as their own alternate (mini) forms.
Split half- cut test in two, compute correlation. Then correct for short test
with Spearman Brown Prophecy Formula.
Alpha - only one estimate. Theoretically estimates the expected correlation
with a "randomly parallel" test.
Internal and External Validity
- both are about the quality of inference or meaning of the study.
Internal validity is about whether the study shows what it says - did the IV cause changes
in the DV or is there some other explanation?
External validity is about whether the results apply to other situations that weren't part of
the study, that is, whether the study results generalize to other situations or contexts.